The present invention relates to direct contact steam injection heaters that use full pressure steam. More particularly, the invention relates to a direct contact steam injection heater for heating certain types of slurries that contain abrasive material.
In direct contact steam injection heaters, steam is directly mixed into a flowing stock (e.g. liquid or slurry) being heated. Direct contact steam injection heaters are very effective at transferring heat energy to the flowing stock. They provide rapid heat transfer with virtually no heat loss to the atmosphere, and also transfer both the latent and the available sensible heat of the steam to the liquid slurry.
The present invention was developed during ongoing developmental efforts by the assignee in the field of direct contact steam injection heaters. U.S. Pat. No. 5,622,655 entitled “Sanitary Direct Contact Steam Injection Heater And Method” by Bruce A. Cincotta et al., issuing on Apr. 22, 1997, U.S. Pat. No. 5,842,497 entitled “Adjustable Direct Contact Steam Injection Heater”, by Brian Drifka and Bruce A. Cincotta, issuing on Dec. 1, 1998, and U.S. Pat. No. 6,361,025 entitled “Steam Injection Heater With Transverse Mounted Mach Diffuser”, issuing on Mar. 26, 2002 represent some of the prior developments in direct contact steam injection heaters by the assignee, and are hereby incorporated by reference.
These types of direct contact steam injection heaters use full pressure steam (i.e. the full amount of steam pressure available), and modulate the amount of steam added to the flowing liquid or slurry by a nozzle and plug configuration. The steam exits through the nozzle under sonic choked flow conditions. The high speed steam from the nozzle shears the flowing liquid or slurry, and creates a homogeneous blend in a combining region located downstream of the nozzle. As heat is transferred, the steam condenses.
Another direct contact steam injection heater was developed by the assignee for heating purified water or other liquids in which steam bubbles tend to merge to create large steam bubbles prior to condensing. This direct contact steam injection heater is disclosed in U.S. Pat. No. 6,082,712, and incorporated herein by reference. This direct contact steam injection heater employs a Mach diffuser. The Mach diffuser injects a sonic velocity steam into the liquid stock through a plurality of relatively small steam diffusion holes. The Mach diffuser is generally coaxial with the heater body and resides within the inlet of a combining region. The purified water or other liquid flows in a radial direction through the inlet into the combining region and turns at an essentially right angle to flow through the combining region. The steam exits the coaxial Mach diffuser as small jets of steam injecting partially into the axial flow through the combining region. The velocity of the liquid flowing through the channel between the Mach diffuser and the combining region is maintained at a relatively high velocity (i.e., a relatively small flow area in the channel compared to the downstream portion of the combining region).
Although the transverse mounted Mach diffuser shown and taught by U.S. Pat. No. 6,361,025 is effective and efficient for heating a flow of slurry in an in-line configuration to eliminate the requirement that stock flow negotiates sharp turns, additional difficulties are presented when attempting to heat the flow of slurry having abrasive materials, such as fine sand particles or other similar components.